Semiconductor component and a method for identifying a semiconductor component

ABSTRACT

The invention concerns a semiconductor component and a method for identifying a semiconductor component that comprises at least one semiconductor substrate equipped with electronic/electromechanical components, which said semiconductor substrate—except for its leads—is embedded in a housing part made of plastic. It is proposed to equip the semiconductor substrate located in the housing part with an identifier located directly or indirectly thereon that makes it possible to distinguish the semiconductor component from other similarly-designed semiconductor components, and which can be read out from outside the housing part using ultrasound. In the case of semiconductor substrates produced in panels, the identifier makes it possible to determine the original position of the semiconductor substrate of a selected semiconductor component on a base substrate on which a plurality of semiconductor substrates were produced, even after the semiconductor substrates have been diced and placed in a housing part.

BACKGROUND OF THE INVENTION

The invention concerns a semiconductor component and a method foridentifying a semiconductor component.

It is generally known that semiconductor components can be produced in apanel on a common base substrate such as a silicon wafer. After thesemiconductor substrates individually equipped withelectronic/electromechanical components are produced, they are diced,which can take place by cutting up the base substrate. The individualsemiconductor substrates are then placed on the mounting area of a leadframe and joined with contact sections of the lead frame using bondingwires. In a spraying procedure known as “transfer molding”, alsoreferred to as transfer forming, the semiconductor substrate is thenembedded—except for its leads formed by the contact portions—in ahousing part made of a mold compound. This procedure is described, forexample, in “Advanced Microsystems for Automotive Applications 99, D. D.Ricken, W. Gessner, pg. 126ff”.

It is often necessary to identify the original position of an individualsemiconductor substrate on the base substrate after dicing andproduction of the finished semiconductor components. This can benecessary, for example, in order to compare preliminary measurementresults carried out on the base substrate with final measurement resultscarried out on the finished, diced semiconductor component. It istherefore desirable to be able to identify the individual semiconductorsubstrates on the base substrate. Optically detectable identificationcodes on the semiconductor substrates have the disadvantage that theycan no longer be identified after the semiconductor substates areembedded in the housing part. For this reason, the mold compound mustfirst be partially removed, e.g., by etching, so that the identificationcode of the semiconductor substrate is optically detectable and can beevaluated. The opened and partially destroyed semiconductor element isthen no longer usable.

SUMMARY OF THE INVENTION

The semiconductor component according to the invention has the advantagethat the semiconductor component can be identified and the originalposition of the semiconductor substrate—on the base substrate—containedin the semiconductor component can be identified without destroying thesemiconductor component. This is achieved by means of an identifierlocated directly or indirectly on the semiconductor substrate that canbe read out using ultrasound from outside the housing part of thesemiconductor component. In doing so, full advantage is taken of thefact that the plastic compound of the housing part is permeable toultrasound, so that an image of the surface structure of thesemiconductor element equipped with the identifier can be generatedusing an ultrasonic device by measuring different trajectories of theirradiated ultrasonic waves or by measuring the ultrasonic wavesreflected on the semiconductor component. Said image is then evaluatedin order to identify the semiconductor component.

In principle, the identifier can be produced in various ways. It isparticularly simple, however, when the identifier is formed by a patternof recesses in a surface section of the semiconductor substrate or acomponent located thereon. The recesses can be produced by etching, forexample. This is particularly advantageous in the case of semiconductorsensors with which the electronic/electromechanical components on thesensor are formed by etching micromechanical structures and are coveredwith a cap piece that is also produced by etching. The recesses can thenbe formed advantageously on an inner side—facing the semiconductorsubstrate—of the cap piece located on the semiconductor substrate. Thisis particularly advantageous when the plastic material of the housingpart is acoustically well adapted to the material of the semiconductorsubstrate and the cap piece. In this case, the ultrasonic wave isreflected only slightly on the boundary layer between the housing partand the semiconductor substrate and/or the cap piece. A gas or vacuum iscontained in the hollow space formed by the semiconductor substrate andthe cap piece, so that an acoustic mismatch always exists on theboundary surface between the inside of the cap piece and the hollowspace. The identifier located on the inside of the cap piece istherefore particularly easy to detect using an ultrasonic microscope.Using anisotropic etching, it can be achieved that the interior walls ofthe recesses are tilted at an angle relative to the surface section inwhich the recesses are produced, so that the ultrasonic waves areadvantageously reflected obliquely to the direction of arrival in theregion of the recesses.

In another exemplary embodiment it is provided that the identifierlocated on the semiconductor substrate or the component is formed by apattern that is composed of a material layer or a layer system ofvarious materials in which ultrasound propagates at a different speedthan in the material of the semiconductor substrate or the component. Inthis case, advantage is taken of the fact that the application of such apattern results in an acoustic mismatch of reflectivity, so that anultrasonic wave is reflected differently on the boundary surface betweenthe pattern material and the semiconductor substrate or component,and/or on the boundary surfaces of two layers of a structured layersystem forming the pattern than on the points of the surface of thesemiconductor substrate on which the pattern is not provided.

According to another exemplary embodiment, the reflectivity of theultrasonic wave is changed by changing the adhesive strength of thehousing material on the semiconductor substrate. Advantageously, thehousing part can be made of a mold compound, and the identifier locatedon the semiconductor substrate or a component located thereon is formedby means of a pattern composed of a material to which the mold compoundadheres more poorly than to the material of the semiconductor substrateor the component. This can be achieved, for example, by forming theidentifier out of a pattern of silver spots. By delaminating the moldcompound at the points of the surface of the semiconductor substrateequipped with the silver spots, the relectance of the irradiatedultrasonic wave changes, so that the identifier can be read out using anultrasonic receiver.

It is also possible to form the identifier located on the semiconductorsubstrate or a component located thereon by means of a pattern composedof a material to which the mold compound adheres better than to thematerial of the semiconductor component or the component. For example,the identifier on the semiconductor element can be formed by means of apattern of polyimide spots to which the mold compound of the housingpart adheres better than to the semiconductor substrate.

Furthermore advantageous is a method for identifying a semiconductorcomponent that comprises at least one semiconductor substrate equippedwith electronic/electromechanical components that, together with aplurality of further semiconductor substrates, is produced on a commonbase substrate in a panel, whereby the semiconductor substrates, afterproduction, are diced and placed on a lead frame and, finally, exceptfor their respective leads, are enclosed in a housing part, and in whichall semiconductor substrates in the panel—before dicing—are equippedwith an identifier identifying the position of the respectivesemiconductor substrate on the base substrate, which said identifier islocated directly or indirectly on the semiconductor substrate, and theidentification of a selected semiconductor substrate—after dicing andplacement in the housing part—is read out using an ultrasonic devicefrom outside the housing part to identify the semiconductor component.An ultrasonic microscope can be used advantageously as the ultrasonicdevice.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are presented in the drawings andare explained in the description hereinbelow.

FIG. 1 shows a cross-section through a semiconductor element accordingto the invention having an ultrasonic identifier located on the innerside of a cap piece,

FIG. 2 shows a top view of a semiconductor element panel,

FIGS. 3a and 3 b show a cross-section and a top view of a semiconductorsubstrate equipped with a cap piece before placement in a housing part.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a cross-section of a semiconductor element according to theinvention. The semiconductor element 1 shown can be an accelerationsensor or a motor vehicle, for example, and includes a semiconductorsubstrate 4, known per se, made of silicon, for example, on the top side17 of which electromechanical structures 13 are produced in an etchingprocess. The structures 13 on the semiconductor substrate are coveredwith a cap piece 5 that is also made of a semiconductor material, e.g.,silicon, and that is interconnected with the semiconductor substrate bymeans of a perimeter seal made of glass or in another fashion. The cappiece 5 comprises a recess 6 produced in an etching process that islocated above the structures 13. Furthermore, conductor tracks 15 forthe electrical contacting of components 13 are located on the top side17 of the semiconductor substrate 4.

Production of the semiconductor substrate is typically carried out in apanel on a common base substrate that is a silicon wafer, for example. Asection of such a base substrate 7 is shown in FIG. 2. The individualsemiconductor substrates are produced in a panel on the base substrate,whereby each semiconductor substrate is equipped with electronic and/orelectromechanical components 13 and conductor tracks 19. Each of thesemiconductor substrates 4 is then covered with a cap piece 5 and diced.Dicing usually takes place by cutting up the wafer. The semiconductorsubstrates 4 are then placed individually with the bottom side 18 downon a mounting area of a lead frame, and the conductor tracks 19 of thesemiconductor substrates 4 are joined with contact sections 11 of thelead frame via bonding wires 16. The contact sections 11 of the leadframe are then separated from each other by means of stamping orcutting, and the semiconductor substrate 4—together with the cap piece 5in a molding tool—is enclosed—except for the ends of the contactsections 11—in a housing part 8 made of a mold compound. The moldcompound can be a thermosetting plastic, for example. The finishedsemiconductor element 1 is shown in FIG. 1.

In the case of an exemplary embodiment of the semiconductor elementaccording to the invention, it is provided that the inner side 22 of thecap piece 5 is provided with an identifier 20 composed of a pattern ofnotch-like recesses 21. The recesses 21 can be formed by etching the cappiece and preferably comprise interior walls that are oblique relativeto the inner side 22 of the cap piece 5. The identifier 20 contains acode, e.g., a binary code, with which the original position of thesemiconductor substrate 4 on the base substrate can be identified. Afterenclosure in the mold compound, the identifier 20 can no longer beoptically detected. Since the semiconductor components 1 do not differfrom the outside, it is impossible to optically identify a selectedsemiconductor component. The identifier 20 can be read out withoutopening the housing part 8, however, by injecting an ultrasonic wave bymeans of an ultrasonic device that comprises an ultrasonic transmitterand an ultrasonic receiver. Since the ultrasonic wave penetrates thehousing part 8, an image of the surface section 22 having the identifier20 can be generated and evaluated by measuring differences in thetrajectory of the irradiated and received ultrasonic wave or bymeasuring reflection differences. Since the ultrasonic wave is reflecteddifferently on the recesses 21 than on the surface section 22, theidentifier is detected by the ultrasonic device and it can be imaged. Anultrasonic microscope is preferably used for this. By evaluating theidentifier, it is possible to determine the original position of thesemiconductor substrate 4′ embedded in the semiconductor component onthe base substrate 7.

The identifier 20 can also be located on the side of the cap piece 5facing away from the semiconductor substrate 4, as shown in FIG. 3a andFIG. 3b. It is further possible to also locate the identifier 20directly on the semiconductor substrate 4. Moreover, the identifier 20does not necessarily have to be formed by means of recesses. It is alsopossible, for example, to form the identifier located on thesemiconductor substrate or a component located thereon by applying apattern and/or a structured coating. The coating can be composed of asingle material layer or a layer system of various materials in whichultrasound propagates at a different speed than in the material of thesemiconductor substrate or the component.

According to a further exemplary embodiment, the reflectance of theultrasonic wave is influenced by changing the adhesive strength of thehousing material on the semiconductor substrate. For example, theidentifier located on the semiconductor substrate or a component locatedthereon can be formed by means of a pattern composed of a material towhich the mold compound adheres more poorly than to the material of thesemiconductor substrate or the component. This can be achieved, forexample, by forming the identifier by means of a pattern of silverspots. By delaminating the mold compound at the points on the surface ofthe semiconductor substrate equipped with silver spots, the reflectanceof the irradiated ultrasonic wave changes, so that the identifier can beread out using an ultrasonic receiver. Correspondingly, it is possibleto form the identifier located on the semiconductor substrate or acomponent located thereon by means of a matter composed of a material towhich the mold compound adheres better than to the material of thesemiconductor component or the component. For example, the identifiercan be formed on the semiconductor component using a pattern ofpolyimide spots to which the mold compound of the housing part adheresbetter than to the semiconductor substrate.

What is claimed is:
 1. A semiconductor component comprising at least onesemiconductor substrate (4) equipped with electronic/electromechanicalcomponents (13), which said semiconductor substrate—except for its lead(11)—is embedded in a housing part (8) made of plastic, wherein thesemiconductor substrate (4) located in the housing part (8) is equippedwith an identifier (20) located directly or indirectly on thesemiconductor substrate (4) that makes it possible to distinguish thesemiconductor component (1) from other similarly-designed semiconductorcomponents, and which can be read out from outside the housing part (8)using ultrasound but that is optically undetectable from outside thehousing part (8).
 2. The semiconductor component according to claim 1,wherein the identifier (20) is formed by a pattern of recesses (21) in asurface section (15, 22) of the semiconductor substrate (4) or acomponent (5) located thereon.
 3. The semiconductor component accordingto claim 2, wherein the recesses (21) are produced by etching.
 4. Thesemiconductor component according to claim 2, wherein the interior wallsof the recesses (21) are oblique relative to the surface section (15,22).
 5. The semiconductor component according to claim 1, wherein therecesses (21) are formed on an inner side (22)—facing the semiconductorsubstrate (4)—of a cap piece (5) located on the semiconductor substrate(4), which said cap piece (5), together with the semiconductor substrate(4), forms a hollow space (6).
 6. The semiconductor component accordingto claim 1, wherein the identifier located on the semiconductorsubstrate or the component is formed by a pattern composed of a materiallayer or a layer system of various materials in which ultrasoundpropagates at a different speed than in the material of thesemiconductor substrate or the component.
 7. The semiconductor componentaccording to claim 1, wherein the housing part is made of a moldcompound, and the identifier located on the semiconductor substrate or acomponent located thereon is formed by a pattern that is composed of amaterial to which the mold compound adheres more poorly than to thematerial of the semiconductor substrate or the component.
 8. Thesemiconductor component according to claim 7, wherein the identifier isformed by a pattern of silver spots.
 9. The semiconductor componentaccording to claim 1, wherein the housing part is made of a moldcompound, and the identifier located on the semiconductor substrate or acomponent located thereon is formed by a pattern that is composed of amaterial to which the mold compound adheres better than to the materialof the semiconductor substrate or the component.
 10. The semiconductorcomponent according to claim 9, wherein the identifier on thesemiconductor component is formed by means of a pattern of polyimidespots.
 11. A method for identifying a semiconductor component thatcomprises at least one semiconductor substrate (4) equipped withelectronic/electromechanical components (13) that is produced on a paneltogether with a plurality of further semiconductor substrates (4) on acommon base substrate (7), whereby the semiconductor substrates (4),after manufacture, are diced and placed on a lead frame (11, 12) and,finally, are enclosed in a housing part (8)—except for their respectiveleads (11)—made of plastic, wherein, before dicing, all semiconductorsubstrates (4) on the panel are equipped with an identifier(20)—directly or indirectly on the semiconductor substrate—identifyingthe position of the respective semiconductor substrate on the basesubstrate (7), and the identifier (20) of a selected semiconductorsubstrate (4′), after dicing and placement in the housing part (8), isread out using an ultrasonic device from outside the housing part (8) toidentify the semiconductor element (1).
 12. The method according toclaim 11, wherein an ultrasonic microscope is used as the ultrasonicdevice.